Thermal insulation and support system for vacuum-jacketed containers



1967 J. M. LESTER 3,347,056

THERMAL INSULATION AND SUPPORT SYSTEM FOR VACUUM-JACKETED CONTAINERS Filed April 26, 1965 4 Sheets-Sheet 1 F/G g g JAMES M. LESTER INVENTOR.

ATTORNEY Get. 17, J LESTER THERMAL INSULATION AND SUPPORT SYSTEM FOR VACUUM-JACKETED CONTAINERS Filed April 26, 1965 4 Sheets-Sheet 2 JAMES M. LESTER INVENIOR.

ATTORNEY J. M. LEST R THERMAL INSULATION AND SYJFPORT SYSTEM FOR VACUUM-JACKETED CONTAINERS Filed April 26, 1965 4 Sheets-Sheet 3 R T Sm mm m E M x w a m J a X V \5 l mm N z am A w a [k b NM H hm x 1% i vm 4 (A V. a w f S 1 mm 0% mv mm i x I mv H mm mm mm av 8 mm mv we 9 ,Q

ATTORNEY Get. 17, 1967 J M LESTER 3,347 %6 THERMAL INsUbATIN AND SUPPORT SYSTEM FOR VACUUM-JACKETED CONTAINERS 4 Sheets-Sheet 4 Filed April 26, 1955 JAM ES M. LESTER INVENTOR.

ATTORNEY United States Patent 3,347,056 THERMAL INSULATION AND SUPPDRT SYSTEM FOR VACUUM-JACKETED CGNTAINERS James M. Lester, Boulder, (1010., assignor to Beech Aircraft Corporation, Wichita, Kama, a corporation of Delaware Filed Apr. 26, 1965, Ser. No. 450,655 8 Claims. (Cl. 62-45) ABSTRAQE OF THE DISCLOSURE This invention relates generally to a pressure storage tank assembly which includes an inner pressure tank, usually spherical, enclosed within a similarly shaped larger sealed outer tank in non-contacting relationship, with the space between the two being evacuated to reduce the travel of heat from the atmosphere through the outer and inner tank walls to the liquid stored in the inner tank. In such assemblies various types of means are used to support the inner tank in relatively fixed position with relation to the outer tank, and to transmit loads from the inner to the outer tank, the outer tank being suitably supported or anchored to fixed structure.

More particularly the invention relates to a novel means for supporting and transmitting loads from the inner to the outer tank, and for reducing to a minimum the travel of heat by either conduction or radiation from the atmosphere through the vacuum space surrounding the inner tank to the liquid it contains.

One of the best rated means presently used for both insulating and supporting an inner tank within an encasing outer tank is a thick layer of insulation completely encasing the inner tank, filling the space between the inner and outer tanks, and pre compressed between the two at a pressure of about 1 psi. into firm contact with the respective outer and inner surfaces of the two tanks. The insulation consists of alternate thin laminations of metal foil and fiber glass wool in a layer about two inches thick. At least one or possibly both surfaces of the foil are highly reflective.

With such a construction the layer of insulation not only serves as a heat transfer barrier but must also serve as a structural member to transmit loads in any direction from the filled inner tank to the wall of the outer tank. When a tank assembly so constructed is used to carry liquid oxygen fuel for a space vehicle, for instance, the tank assembly is necessarily subjected during vehicle takeoff to as high as 20 times the normal force of gravity. This results in the application by the inner tank of a large total compression load over a relatively large area of the tank encasing insulation layer. While such compression load per square inch of insulation surface area is not excessive, it is an accepted fact that the thermal conductivity (k) for such fiber glass mat-foil laminates increases at a much faster rate under low compression loads and at much slower rate under high compression loads. Thus the thermal conductivity radially through the compressed insulation layer between the tanks increases to several times its conductivity at the initial pre-load of approximately 1 lb. per square inch. Since the insulation area over which the increase in conductivity occurs is large, there is consequently a very large increase in the total heat units (B.t.u.) passing through the insulation layer by conduction and reaching the liquid in the inner tank. The described conventional construction is not, therefore, efficient in performing its function of reducing heat transfer to a minimum.

The present invention is based on the following reasoning:

That the total radial heat transfer per unit of time through a layer of insulation comprised of alternate laminations of reflective radiation shields and fibrous conduction insulating separators is relatively high when a large area of the laminated insulating material is subjected to even a relatively low compression load per square inch, as when the insulating material is also required to serve as the support and load transfer member between an inner tank and a surrounding outer tank assembly;

That the total heat transfer per unit of time through such laminated insulation can be greatly reduced by re ducing by or more the surface area of the insulation layer through which forces and loads are transmitted from the inner tank to the outer tank even though the load per square inch on the reduced area of insulating material is greatly increased;

That the voids created in the space between the two tanks by the reduction in area and volume of the insulating material can be more efficiently insulated against the travel of radiant heat by the use of load-free, highly reflective radiation barriers suspended in such void spaces out of contact with the walls of both tanks; and

That the permitted total of heat units which reach the liquid in the inner tank per unit of time through such a modified inner tank supporting and insulating system, will consequently be very materially less than if the insulating material is in continuous compression loaded contact with both the inner and outer tanks, and must also serve as the inner tank supporting and load transferring member.

It is an important object of the invention to provide a truss type laminated inner tank support and load transfer member for a double walled tank assembly which is in actual contact with less than 50% of the exterior surface area of the inner tank; which is not in direct contact with any part of the outer tank but transmits its load to the outer tank through insulation isolated widely separated bolt attachments; which has a very low coefiicient of heat conductivity due to the lamination material and arrangement, and which will withstand compression, tension and buckling loads, lamination separating loads, and bending and shear loads from any direction.

Another object is to provide, in combination with the above mentioned truss type support, a system for insulating those portions of the vacuum space 'between the tanks which are not occupied by the frame members of the truss which will intercept, block and reflect thermal radiation entering the vacuum space through the outer tank wall, and which will additionally dispose of heat units traveling by either conduction or radiation by utilizing cold vapor escaping from the inner tank to absorb and carry off such heat units.

An additional object is to provide, in conjunction with the above identified truss type laminated tank support, an arrangement of sectional vapor cooled heat radiation shields which are suspended in the vacuum space between an inner and outer tank assembly in such a manner that no shield is in heat conducting contact with any other shield or with the surfaces of either the inner or outer tanks.

Another object is to provide an insulation and support system for the vacuum jacketed inner tank of a double walled tank assembly which system, in total, weighs approximately 16% of the weight of insulation and support systems now in common use.

It is a further general object of the invention to provide a combination insulation and support system for the inner tank ofa double walled tank assembly which is so emcient that the heat transmission to liquid oxygen in a 28-inch diameter inner tank is an external environment of 76 F. is reduced to as little as 3 B.t.u. per hour total.

The invention, together with other objects explained herein, will be more clearly understood when the following description is read in connection with the accompanying drawings, in which:

FIG. 1 is a top plan view of a double walled storage vessel embodying my invention, the top half of the outer shell having been removed to show details of the inner tank supporting and insulating structure, certain heat shields being shown in section;

FIG. 2 is a perspective view of the inner vessel only, and shows additional details of the skeleton truss which serves to transmit loads from the inner tank to the outer supporting shell, the outer shell having been removed for this view;

FIG. 3 is a side elevation of the completely assembled storage vessel mounted in a suitable fixed supporting base, the base being shown in transverse vertical section;

FIG. 4 is a fragmentary enlarged scale view of a portion of the skeleton load transferring truss, andshows details of One structural means for applying tension to the truss members;

FIG. 5 is an enlarged scale perspective ,viewof the complete storage vessel assembly shown in FIG. 3, certain portions being cut away and removed to disclose certain details of construction;

FIG. 6 is an enlarged scale, fragmentary, transverse sectional view taken along the line 66 of FIG. 1, and shows details of the laminated truss construction, one of the bolt anchors through which loads are transmitted from the truss to the outer shell, and an arrangement for suspending reflective heat shields between the inner and outer shells;

FIG. 7 is a fragmentary perspective view showing detals of a preferred manner of suspending reflective heat shields from the truss with their marginal surfaces in contact with fill and delivery tubes;

FIG. 8 is a perspective view of the upper half of a tensioning cap strip which constitutes the outer lamination of the truss, and which cooperates with a like lower half, not shown;

FIG. 9 is a fragmentary transverse sectional view through the truss, and is taken along the line 9--9 of FIG. 1; and

FIG. 10 is a schematic view showing in flat pattern the.

five compartments defined by the truss on the exterior surface of the inner stroage vessel, and particularly shows a preferred routing of both the fill or inlet pipe and the combination vent and fluid discharge pipe.

The invention is disclosed herein embodied in a double walled tank assembly particularly designed as a fuel tank for a space vehicle, to store liquified oxygen, which begins to vaporize at a temperature of 183 C., or liquified hydrogen, which begins to vaporize at a temperature of 252.7 C.

The illustrated tank assembly embodying the invention will first be described generally, and a detailed description of certain individual components, their construction, and their functional cooperation will follow.

Generally the structure embodying the invention includes:

(l) A spherical metal inner pressure-liquid storage tank (FIGS. 1, 2 and 5) within which is rigidly secured a perforated large diameter pipe 21 (FIG. 5) which extends internally from the north pole to the south pole of the inner tank, and the upper end 22 of which proell 4 jects slightly outside the tank wall and is capped and sealed. Filler and fuel delivery tubes 23 and 24 communi.- cate interiorly with the projecting upper end 22 of pipe 21 below its cap. The exterior surface of tank 20 is highly reflective. Depending on the type of metal used for the inner tank, the reflective surface can be provided by polishing, plating with silver, gold or copper, or by applying a metal coated plastic film or metal foil;

(2) A spherical metal outer tank or shell 25 of larger diameter, which concentrically encloses the inner tank.

Tank25 is made in two halves which are pressure sealed together, as by welding, and which is also pressure sealed at all bolt and tube entry points, and at all seams, if

any. The space between the two tanks is evacuated to provide a vacuum insulating jacket for the inner tank. A highly reflective inner surface is also provided for the outer tank, as by polishing, silver plating, etc., as described for the inner tank. The outer surface of the outer tank may also be made highly reflective, if desired, although this is not usually necessary. The outer tank is rigidly secured, as by a Welding seam 26, to a fixed structural base or support member 27 (FIG. 3) which may be of any suitable design or configuration;

(3) A means for supporting and maintaining the inner tank in fixed position with relation to the outer tank, for transmitting loads to the outer tank and to the base 27, regardless of the direction of the load forces.

This means is in the form of a skeleton type laminated truss, designated as a whole by the numeral 28, FIGS. 1, 2 and 5, which tightly encases the inner tank 20. This truss consists of two opposed generally triangular loops 29, one at the north pole or top of the tank encircling the projecting pipe end 22, and one at the diametrically opposite south pole of the tank. Three integral legs 30,

31 and 32 connect the loops 29 and complete the truss:

framework. The number of legs may be increased, if desired, but three legs have proven ample to transmit and distribute the loads to which the truss is subjected.

The transverse width of all truss frame members is pref- This materially reduces the transfer of heat radiallythrough the truss by conduction. It also provides ample space between the outer surface of the truss and the adjacent wall of outer tank 25 to accommodate the circuitously routedfuel delivery and vent tube 24, which is passed from one to the other of the various compartments 33, 34, 35, 36and 37 (FIG. 10) into which the truss frame members divide the outer surface of inner tank 20.

Truss 28'is capped by a cap strip 38 (FIGS. 8 and 9) which is formed in two complemental mating halves, the

upper half being shown in FIG. 8. As a means of transferring loads from the truss 28 to the wallet outer tank 25, cap strip 38' carries internally threaded conduction insulated bolt anchor socket 39, FIGS. 6 and 8, preferably at six widely spaced locations on the truss framework. The locations of three sockets, as indicated by the numerals 40, 41 and 42, FIGS. 1, 2 and 8, are near the respective angles of the upper loop 29. The other three sockets are at corresponding locations near the respective angles of the lower loop, not visible.

Again referring to FIG. 6, a washer 43 surrounds each socket 39 and is preferably welded thereto and to the cap strip 38, as indicated by the numeral 44. Each washer 43 carries a thick series 45 of highly polished metal laminations or shims which surround and are held in position by the sockets 39.

The wall of tank 25 is provided with circular apertures 46 of larger diameter than the sockets 39, and at loca tions to register concentrically with such sockets, as shown. Dished washer 47 are welded, as at 53, to the exterior surface of tank 25, with their central apertures registering concentrically with the tank wall apertures 46. When all tank apertures 46 are properly aligned with their respective sockets 39, bolts 48 are firmly seated in the respective threaded sockets 39 to compress the series of shims 45 against washer 43. A weld seam 49 is then applied entirely around each bolt head 48 to seal the entire bolt attachment anchor point against leakage under vacuum. It will be seen that the described bolt anchor construction provides only a very restricted area of solid conduction between the outer tank wall and the cap strip of the truss;

(4) A means for reducing to a minimum the travel of radiant heat units through the exterior tank wall, through that portion of the vacuum space which is not occupied by the truss, and through the inner tank Wall to the liquid it contains.

Such a means includes radiant heat barriers or shields, 50 51, 52 and 54 (FIGS. 1, 6 and 9), at least one for each of the compartments 33, 34, 35, 36 and 37 (FIG. defined by the truss frame members. These heat shields have sufficient rigidity to be self supporting when suspended at their marginal edges between the walls of the inner and outer tanks 20 and 25, within the respective compartments 33-37 defined by the loops and legs of the truss 28. Each heat shield is of such configuration that its edges lie adjacent but spaced slightly from the respective truss members which define its compartment. Thus no heat shield is in heat conductive contact with any other heat shield.

Each heat shield has a highly reflective coating of silver, gold, copper or the like, and functions as an almost pure reflector of radiant heat; and

(5) A means for supporting the marginal edges of each heat shield from the respective adjacent truss members which define its compartment, and for maintaining a surface of each marginal edge of each heat shield in bonded contact with the wall of the vapor discharge and delivery tube 24 which extends around the periphery of each truss defined compartment, as illustrated in FIG. 10. The heat shields are thus cooled by conduction through the wall of tube 24, which in turn is maintained at an extremely low temperature by the vapor which it contains. The tube 24 and the adjacent tube cooled marginal portions of each heat shield thus serve to dissipate a major portion of any radiant heat units which penetrate into the evacuated space between the inner and outer tanks and reach the heat shields.

The shield supporting means includes spaced tabs 55, 56 and 57 (FIGS. 6 and 9) extending outwardly integrally from vertically spaced rigid laminations which form the various truss members, combined with looped tube clamps 58, 59 and 60, one connected to each tab by means of rivets, brads or bolts which pass through the edge of the heat shield, the tab, and the clamp. A suitable cement is used to bond the edges of each heat shield to the adjacent portions of the tubing in the areas between clamps. The clamps thus serve to support the tubing and maintain its spacing between the walls of the inner and outer tanks, and adjacent the truss members, and also aid in maintaining the tubing and edges of the heat shields in bonded contact.

Load transmitting truss construction Referring particularly to FIG. 6, the skeleton-like truss 28 is built up from a series of alternated structural laminae 61 and insulating separator laminae 62. These laminae will be hereinafter called sections. Each section, both structural and separator, is pre-cut to a spider-like configuration generally similar to the cap strip shown in FIG. 8, with a loop and three depending legs. The structural strips are formed to a channel or other irregular cross section, as shown in FIG. 6, so that they will nest one atop the other with the separator sections 62 between them. They are formed of a metal alloy or plastic which has relatively low solid thermal conductivity, and high resistance to internal heat flow. Stainless steel or titanium alloys are suitable. To provide the necessary structural strength and rigidity, the structural sections 61 are preferably about .01" in thickness as opposed to .001" thickness for the foil used in an ordinary foil and fibre glass insulating mat. Both surfaces of the structural sections are provided with a highly reflective coating such as silver, gold, copper or the like and each therefore constitutes a radiation barrier.

The insulating separator sections 62 are formed of soft fiber glass wool which is not compressed prior to assembly. The separator sections are thin enough to give the assembled legs and loops of the truss high strength, but are thick enough and tough enough to practically eliminate the formation of wrinkles and bumps which might otherwise form in the structural sections when the entire truss is placed under compression against the outer surface of inner tank 20, as will be explained. Furthermore, should a wrinkle or wrinkles form in any of the structural sections, the adjacent separator sections are sufliciently thick and tough to prevent penetration by the wrinkle, and consequent contact with any adjacent structural section to produce an area of high heat conductivity. A thickness of .06" has been found adequate for the separator sections 62.

The use of considerably thicker separator sections than are used in the ordinary foil and fiber glass insulating mat naturally results in greater spacing for the structural sections 61. This greater spacing reduces any tendencies for adjacent reflective surfaces to amplify heat flow due to constructive interference of electromagnetic waves.

The separator sections 62, of course, constitute low heat conductive, heat insulating mats for reducing to a minimum the transfer of heat by conduction between the reflective metal radiation barriers 62.

The assembled structural and separator sections which form the truss provide low thermal conductivity through the various integral truss members crosswise, radially and lengthwise, even under compression loads. The structural sections also impede the passage of radiant heat radially through the truss members without noticeably increasing solid heat conductance radially through the truss frame members. Furthermore, in the structure illustrated, the relatively small transverse dimension across each of the assembled truss frame members results in actual cont-act by the truss of only about 5% of the total surface area of the inner tank 20. In other Words the area of the potential path of solid heat conductance is reduced by approximately by using the described skeleton load transmitting truss, as opposed to using a complete covering of insulating material which fills the space between the two tanks.

In assembly, a suitable spacer 63 is positioned in the void created by the channel section shape of the metal sections, to give adequate radial central support. The first structural sections are assembled on the outer surface of the inner tank wall as mating upper and lower halves, identically oriented. The corresponding adjacent legs of each half are placed under tension simultaneously by suitable tools, and their respective adjacent ends are bonded to each other. Separator sections of identical configuration are then applied over the previously positioned structural sections and their mating surfaces are bonded to each other. This build up of alternate structural and separator sections continues until the desired truss thickness is obtained, each of the mating structural sections being placed in tension during application to partially compress the separator sections beneath.

Two complemental mating cap strip sections 38 (FIGS.

6 and 8) are then applied to rest on the surfaces of the topmost structural sections 61 in the assembly. The corresponding legs 64, 65 and 66 (FIG. 8) of the upper and lower cap strip sections are then placed under high tension by bolt and nut assemblies 67 and 68 (FIG. 4) which pass through cooperating angle brackets 69, 70, 71 and 72, which are rigidly secured, as by welding, to the free ends of the legs of the upper and lower cap strip sections 38, as shown. in detail in FIG. 4. By this means the assembled structural sections 61 and separator sections 62 are simultaneously placed under compression against the outer surface of inner tank 20, and the compression load is distributed substantially equally throughout the entire skeleton truss. The tensioned upper and lower cap strip sections 38 serve to prevent possible separation of the structural section laminations 61 under a lengthwise compression load. Their channel section configuration, as shown in FIG. 6, coupled with the channel section configuration of the structural sections 61, serve to greatly improve the resistance of the various truss members to buckling and shear loads.

The cap strip sections 38 may be formed of stainless steel, plastic or titanium, preferably the latter. They are preferably greater in lateral dimension than the built up truss members on which they rest, as shown in FIG. 6.

As previously mentioned, certain of the intermediately located structural sections 61 are provided with spaced integral tabs 55, 56 and 57 which project laterally from one side edge only of thesection. Thus heat cannot be easily conducted from any heat shield through any structural section 61 to an adjacent heat shield. The heat shield supporting tabs can also provide a direct path for conducting heat out of the laminated truss structure and to the vapor discharge tube 24 as well as to the tube cooled marginal portions of the tab supported heat shields 51-52.

In the described tank assembly heat transfer to the stored fluid by gaseous heat conduction and natural convection is negligible because the truss is located in a vacuum environment surrounding the inner tank.

Hence the transfer of heat is only by solid conduction and by radiation. In the tank structure illustrated the described laminated load transmitting truss is in contact with the inner tank 20 over only about 5% of its total exterior surface area, and is not in direct contact with any part of the interior surface area of the outer tank 25. The truss anchors are so constructed as to provide very low solid conductivity from the outer tank to the truss structure. The alternate reflective structural sections 61 and insulating separator sections 62 form a composite truss frame which has very low thermal conductivity. The legs of the truss have relatively great length compared to their width and thickness, and the transmission of any heat which reaches the structural sections 61 will be resisted both radially and lengthwise through the truss.

Heat transfer through the vacuum jacket to the inner tank is stopped by the various highly reflective tube cooled heat shields 51, 52, etc.and additional passive non rigid reflectors as previously explained.

The end result is an insulation and load transfer system for a vacuum jacketed double walled container which has a very low coefficient of heat transfer, either by solid conduction or by radiation. Furthermore, the use of the described truss structure results in a very large saving in weight (approximately 84%) due to the elimination of large quantities of insulation mats which encase the inner tank and fill the space between the two tanks in conventional insulating and load transfer systems.

As. to strength, all the integral members of the described skeleton truss framework have a high moment of inertia about their width and radial thickness axes. The heavy cap strips 38, of greater width than the structural and separator sections 61 and 62, and the tensioning of those cap strips, provide a very high resistance to separation of the laminations under compression and buckling loads, and also provide the entire truss with a to enable those familiar with this art to construct and use it, I claim:

1. A storage tank for liquified gas comprising: i

an inner wall defining a chamber to be maintained at.

an extremely low temperature;

a laminated skeleton truss encompassing and in continuous direct contact with the exterior surface of said inner wall, the total contact area between the inner wall and the truss being of the order of 3% to 50% of the total exterior surface area of the inner Wall, said truss having a low coeflicient of solidheat at spaced locations to maintain the spacing between the outer wall, the truss and the inner wall, and to transmit loads from the truss to the outer wall.

2. The tank construction described in claim 1, and thin radiant heat barriers having a highly reflective surface suspended from and supported by certain of the frame members of said skeleton truss within the separate compartrnents defined thereby, each heat barrier being supported in a position spaced from both the inner wall and the outer wall.

3. The tank construction described in claim 2,

and a vapor discharge and delivery tube in communication with the interior of the chamber defined by said inner wall and extending along the peripheral boundary of the various separate compartments defined by the various frame members of the skeleton truss, and extending continuously from one compartment to the next;

means integral with said truss frame members for supporting said tube in said compartments in a position spaced from both the inner wall and the outer wall; and

means maintaining the marginal portions of each of said heat barriers in surface contact with those portions of the delivery tube which are located within the respective separate compartments.

4. In a vacuum insulated container for storing liquified gas at extremely low temperature, which container includes an inner storage tank enclosed within a sealed outer supporting shell with the walls of the two spaced from each other and the space between the walls being I evacuated, low heat conduction apparatus for maintaining the spacing between the walls of the inner tank and outer shell and for transmitting loads from the inner tank to the outer shell, said apparatus comprising:

a unitary skeleton framework truss of generally symmetrical configuration tightly encasing and in firm contact with the exterior surface of said inner tank over a maximum of not more than 50% of its total surface area; the integral frame members of said truss. defining a plurality of separate compartments on the.

9 18 under tension to compress the various laminae and interior of said inner tank and extending continuously maintain them in position one atop the other; along the periphery of each of said separate comand means carried by said cap strip and projecting outpartments defined by the skeleton members of said ward therefrom and anchored to the wall of the truss, from compartment to compartment, for deouter shell to maintain the spacing between the walls livery of vapor to the exterior of the outer shell; and of the inner tank and the outer shell, and between means connecting the portions of the tube in each sepathe truss proper and the outer shell. rate compartment to the inwardly extending tabs in 5. The apparatus described in claim 4 in which the the respective compartments and to the marginal means projecting outward from and carried by the cap edges of the radiation shield in each compartment, strip consists of a plurality of threaded bolt sockets ex- 10 whereby the tabs serve to support both the tubing and tending to the wall of the outer shell. the shields out of contact with the Walls of the inner 6. The apparatus described in claim 4 in which the thin tank and outer shell, and the vapor tube in contact structural section laminations and the cap strip of the with the marginal portions of the respective shields truss are of irregular and of generally complemental cross serves to cool the shields by conduction. sectional configuration.

7. The apparatus described in claim 4, and References Cited spaced integral tabs projecting into each of the sepa- UNITED STATES PA rate compartments from certain of the structural 2863297 12/1958 Johnston laminations of said truss; and

a highly reflective radiation intercepting shield spanning g fgs each of said separate compartments and connected to and supported by the said tabs in each compartment, out of contact with the Walls of both the inner FOREIGN TQ tank and the Outer m 914,193 12/1962 Great Britain.

8. The apparatus described in claim 7, and

a vapor discharge tube in communication with the LLOYD KING Prlmary Exammer' 

1. A STORAGE TANK FOR LIQUIFIED GAS COMPRISING: AN INNER WALL DEFINING A CHAMBER TO BE MAINTAINED AT AND EXTREMELY LOW TEMPERATURE; A LAMINATED SKELETON TRUSS ENCOMPASSING AND IN CONTINUOUS DIRECT CONTACT WITH THE EXTERIOR SURFACE OF SAID INNER WALL, THE TOTAL CONTACT AREA BETWEEN THE INNER WALL AND THE TRUSS BEING OF THE ORDER OF 3% TO 50% OF THE TOTAL EXTERIOR SURFACE AREA OF THE INNER WALL, SAID TRUSS HAVING A LOW COEFFICIENT OF SOLID HEAT CONDUCTION, AND DEFINING WITH THE EXTERIOR SURFACE OF SAID INNER WALL A PLURALITY OF SEPARATE COMPARTMENTS; A SECOND WALL OUTSIDE AND SPACED FROM THE INNER WALL AND FROM SAID SKELETON TRUSS, THE SPACE BETWEEN THE TWO WALLS BEING SEALED AND EVACUATED; AND SPACED MEANS CARRIED BY AND PROJECTING OUTWARD FROM SAID TRUSS AND RIGIDLY CONNECTED TO SAID SECOND WALL AT SPACED LOCATIONS TO MAINTAIN THE SPACING BETWEEN THE OUTER WALL, THE TRUSS AND THE INNER WALL, AND TO TRANSMIT LOADS FROM THE TRUSS TO THE OUTER WALL. 